The subject matter disclosed herein relates generally to imaging systems, and more particularly to a source side focal spot monitoring device for an imaging system.
Some known imaging systems, such as computed tomography (CT) imaging systems, include an x-ray source and a detector assembly that are coupled to a gantry. In operation, the x-ray source emits a fan-shaped x-ray beam or a cone-shaped x-ray beam toward a subject or object positioned on a table. The x-ray beam, after being attenuated by the subject, impinges upon the detector assembly. The intensity of the attenuated x-ray beam received at the detector assembly is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector assembly produces a separate electrical signal indicative of the attenuated x-ray beam received. These electrical signals are collectively referred to as x-ray attenuation measurements or x-ray images.
Reference normalization is utilized in CT preprocessing operations to reduce or remove the impact of the x-ray source output fluctuation. For this purpose, the conventional detector assembly includes a set of reference channels (also referred to as reference detectors). The reference channels are typically located slightly outside the reconstruction field of view (FOV) of the detector assembly such that the reference channels receive x-ray photons directly from the x-ray source without interference from the scanned subject. In operation, the reference channels monitor the x-ray source flux and the measured signal is applied to the measured projections. The impact of any variations in the x-ray source output on the measured projections is thereby substantially removed.
However, when the CT imaging system is utilized to image relatively larger subjects or objects, the subjects or objects may potentially block a portion of, or all of, the reference channels during the scan. Thus, when the reference channels are blocked, the reference channels receive attenuated x-rays. As a result, the reference channels may generate an invalid normalization value, which degrades the image quality. More specifically, the incorrect normalization may cause streaks and artifacts to appear in displayed images.